Winter 2011 GIS Institute

Winter 2011 GIS Institute

Space:Questions & Tools


Space: Questions• Questions can range from basic to complex:

– How does a variable or phenomenon vary over space? (Can be answered with a map)

– How does distance to public transportation affect house values? (Can be answered using traditional statistical software, with spatial variables created using GIS)

– What is the spatial distribution of foreclosures in Phoenix, AZ? (Can be answered with maps and descriptive spatial statistics)

– What is the impact of foreclosure densities on neighborhood crime? (Can be answered with spatial statistics and models)


Space: Tools• As with any other discipline, geographers

work with a range of “spatial” questions, and there are generally myriad approaches with which to answer those questions

• This week we will focus primarily on developing your comfort level with GIS, Geographic Information Systems– Commonly used for data collection,

management, mapping, and analysis

Rachel Franklin

What is GIS?• Geographic Information Systems or Science– A bringing together of skills, theory, computer

science, database management, and geography

– A collection of:• Hardware• Software• Data • People• Procedures• Network

– An abstraction of reality

Rachel Franklin

Clarke (2001) presents the following definitions:• GIS is “a powerful set of tools for

storing and retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes.”

– Burrough, 1986

Rachel Franklin

• GISs are “automated systems for the capture, storage, retrieval, analysis, and display of spatial data.”

– Clarke, 1995

Rachel Franklin

• A GIS is “an information system that is designed to work with data referenced by spatial or geographic coordinates. In other words, a GIS is both a database system with specific capabilities for spatially-referenced data, as well as a set of operations for working with the data.” – Star and Estes, 1990

Rachel Franklin

• GIS is “a special case of information systems where the database consists of observations on spatially distributed features, activities, or events, which are definable in space as points, lines, or areas. A geographic information system manipulates data about these points, lines, and areas to retrieve data for ad hoc queries and analyses.” – Dueker, 1979

Rachel Franklin

• GIScience is “the generic issues that surround the use of GIS technology, impede its successful implementation, or emerge from an understanding of its potential capabilities.”

- Goodchild, 1992

Source: sutton.gov.uk

Source: krygier.owu.edu


Roles of a GIS (Fotheringham)• Data manipulation• Data integration– Using GIS to create new information that

is then used in other software or analysis environments

• Data visualization– For example, looking at regression

residuals

A brief history of GIS• Cartography, especially thematic maps• Map overlay

– Tyrwhitt’s 1950 chapter in Town and Country Planning Textbook

– McHarg’s 1969 Design with Nature

Source: architectmagazine.com

Rachel Franklin

Brief History Continued…• The Canada Geographic Information

System, mid-1960s• The Census Bureau’s DIME (Dual

Independent Map Encoding), late 1960s• Computerized cartography• Freestanding GIS software packages• Ever-increasing computer power• Ever-increasing quantities of spatial data

Rachel Franklin

What can we do with a GIS?• Make maps• Compute summary statistics• Import, manipulate, and manage

data• Spatial analysis

Early example of spatial analysis: John Snow’s 1854 Cholera Map

Rachel Franklin

Other Examples• Habitat suitability• Hurricane vulnerability• Heat wave vulnerability• Bus stop locations• Smart growth policies

Nice Maps


Interactive Maps

http://www.washingtonpost.com/wp-srv/special/politics/2010-race-maps/house/

Rachel Franklinhttp://www.mappiness.org.uk/

Rachel Franklin

What do you think of this map? The analysis?

Or this one? (Hint: sometimes our spatial research challenges in aren’t necessarily cartographical)


Traditional Spatial Analysis, Redux• Tobler’s First Law of Geography states that,

“Everything is related to everything else, but near things are more related than distant things.”

• Geographers and others have often try to measure the “everything is related to everything else” by looking at connections between pairs of locations or entities– Provides clues about diffusion behaviors, as well as

strength of ties between places– e.g. migration flows, commuter flows, communication

flows


Regionalization • MIT’s SENSEABLE

City Lab used telephone call data from British Telecom to redraw the regional map of Great Britain.


Traditional Spatial Analysis, Redux


Organizing Spatial Data in a GIS• A GIS doesn’t save information as maps– Rather, we tell the GIS how to locate objects

in relation to other objects and in space• Things to be aware of:– Your spatial data model– The relationships your objects have with each

other in the real world• e.g. street intersections or shared state borders• We call this “topology”


Spatial Data Models• Most common are vector and raster

Vector Raster

Polygon

PointLine


Vector Model• Features are stored as points, lines or polygons

– All are combinations of nodes and vertices• Locations are recorded as X,Y coordinates• Each feature – point, line, or polygon – is linked to an

“attribute table” or set of variables– For example, you could have a dataset of cities, represented

as points, and the attribute table might contain characteristics of the city – population, median household income, etc.

• Feature classes – or datasets of spatial objects – contain only the same types of objects– This means only points or lines or polygons– And since they all share the same attribute table, they should

be the same thing• So, no combining cities and septic systems in one feature class, even

though both might be points


Why We Like the Vector Model• Features can be located precisely• We can store lots of information

(variables or attributes) about each feature

• Useful for many types of map-making• Perfect for types of analysis, such as

areas, lengths, or connections


Raster Data Model• Sub-divides a study area into square

pixels – rows and columns• Only need the location of the upper left-

hand corner and all other locations are implicit, assuming you know your pixel size

• Only one value is recorded for each pixel– For example, temperature, precipitation, or

land use type


Why We Like the Raster Model• Best for continuous data• Analysis can sometimes be faster• And some types of analysis require

raster data• “Yes, raster is faster, but raster is

vaster, and vector just seems more correcter.” – Dana Tomlin


Topology – Modeling Feature Behavior

• Topology sets the rules of behavior for features in a feature class

• A classic example is road networks:

• Basic topology rules deal with adjacency, connectivity, overlap, and intersection

Highway Overpass Typical Street Corner


The End…for Now…• Let’s go see the computer lab• And break for lunch• We’ll reconvene at 1:00 pm in CIT

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Documents

Winter 2011 GIS Institute